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Neutron Star
Near its surface, matter in a neutron star resembles what's in a white dwarf. About 1000 m deep into one, nuclear matter takes the form of macroscopic pieces called nuclear pasta. In the highest layer, electrons still occupy most of the volume, but nuclear matter takes the form of meatball sized pieces called gnocci. What does that. The key reaction is fusion of an electron and a proton to form a neutron: e- + p <--> n + nu + (-tbd MeV) the negative sign meaning that the reaction consumes energy. At low pressure, the reaction goes completely to the left. Free neutrons decay with a half-life of (tbd sec). But there is another factor to consider at high pressure. An electron occupies a much larger volume than either a proton or neutron. To push back other electrons from that volume requires that an electron have momentum. If it has momentum, it has energy. It carries that energy into its fusion with a proton. The reaction should be: e- + p <--> n + (-tbd MeV) + Q where Q is the electron's energy. If Q is large enough, the reaction will shift to favor neutron formation. (Neutrinos aren't important here.) Going down a thousand meters into a neutron star shifts that balance from mostly electrons and protons to mostly neutrons. Going down, it takes the form of rods (spaghetti), plates (lasagna), and three dimensional lattices. By that point, about half the volume is nuclear matter and half electrons. Still further down, electrons become bubbles in a sea of nuclear matter. Between 700 m and 1000 meters deep is a layer of microscopic things. I read of things like"bubble nuclei" and see graphs which indicate lowered particle density near the center of a large nuclide (type of atomic nucleus). I picture what lies in that layer as proton-bounded cells in a free-electron environment. Their particle count (A) would be so high that liquid-drop properties would dominate quantum properties. At the same time, these drops of nuclear matter would also be immersed in a dense free-neutron environment. Drop shape is formed by electromagentic interactions with electrons and drop content is regulated by equilibrium between the rate at which neutrons enter and leave a drop. The ratio of electrons to total particles, Ye, is determined by equilibrium between fusion of a proton and electron into a neutron and fission of a neutron into a proton and electron. The energy driving the reaction toward neutrons is the gravitational potential energy released when an electron disappears. Electrons are big at these depths, compared to protons or neutrons. The MeV-scale energy release needed to drive a nuclear reaction which consumes energy happens in the kind of pressure found several hundred meters deep in a neutron star. As pressure declines, the volume the occupy is worth less energy. Equilibrium shifts from favoring neutrons to favoring protons and electrons somewhere in the depth range of 500 and 1000 m. Neutrons stop being dense. Since new neutrons are rarely added to a drop, and since any free neutron within a drop will exit much more quickly, drops will contain only bound neutrons and be nuclei. These are "dripline nuclides", stuffed with all the neutrons they can hold. (under construcrion, 11-10-19)